Continuing on previous week’s topic; a system that can only talk to itself is indeed a lonely system. When Google released its Maps API in 2005, any website could suddenly present beautiful and functional maps, mashed up with any other stored data.
Today, Social Media sites offer a number of API's to allow sharing and posting, and new services emerge every day that are mash-ups of existing tools, using APIs to weave them together. API's are the fabric of the web.